1. Field of the Invention
The present invention relates to a method for dispersing a pigment in a solvent, which is suitable for applications to color filter, RGB pigment paste, inject ink, display, printing on paper, painting on vehicles or furniture, etc.
2. Description of the Prior Art
Most pigments are rigid conjugated-small molecules. Such molecules are usually hard to disperse due to van der Waals force and π-π stacking. Therefore, it's a common issue in applications of pigments how to stably and uniformly disperse the pigments in solvents. Currently, two major solutions are:
(a) Modifying Surface Properties of the Pigments
Through a chemical process, pigment particles can be modified by grafting specific molecules on surfaces of the pigment particles. Such molecules generally have good affinity to solvents, whereby attraction between the pigment particles can be reduced. Thus the modified pigment particles can perform better in terms of dispersibility, paintability, miscibility with the solvent, etc. However, such modification process occurring between a solid phase and a liquid phase normally requires longer reaction time and has a lower conversion rate, which does not facilitate commercialization.
(b) Adding a Dispersant
By adding a dispersant in a proper solvent accompanied with mechanical agitating, coagulated pigment particles can be re-dispersed in the solvent. Different from the above modification process involving covalent bonding, only van der Waals force occurs between the dispersant and the pigment particles. Therefore, it's important but difficult to design a proper dispersant depending on the solvent system and surface features of the pigment particles, when considering the balance between particle-particle interaction and particle-solvent interaction. Such dispersant has to be easily adsorbed on surfaces of the pigment particles for them to be well dispersed.
To improve the above disadvantages, the present invention provides a physical method for dispersing a pigment in a solvent, in which layered or platelet clay is used to separate the pigment particles due to their geometric inhomogeneity or mutually exclusive aggregation.